Extended Forecast Discussion NWS Weather Prediction Center College Park MD 144 AM EST Thu Nov 14 2019 Valid 12Z Sun Nov 17 2019 - 12Z Thu Nov 21 2019 ...Pattern Overview and Guidance/Predictability Assessment... Upper pattern will transition toward western troughing and eastern quasi-zonal flow in about a week after two successive systems lift northeastward along the East Coast. In the West, upper ridging will weaken on Monday as it slides eastward atop a closed upper low moving westward away from Baja California. This will pave the way for a Pacific shortwave to dig through interior California as downstream heights rise in response toward the Ohio Valley. Off the Southeast coast, the models have come into better agreement with a lead surface low offshore Sun-Mon. Kicker trough through the lower MS Valley showed more spread among the guidance with the UKMET/Canadian quicker than the GFS/ECMWF and most of the ensembles. Preferred the GFS/ECMWF-led consensus which was closer to continuity. That kicker trough will likely spin up another sfc low off the coast that will lift northeastward and possibly develop in earnest off or near New England, depending on northern stream flow across the Great Lakes. GFS runs were deeper and closer to the coast than the ECMWF and the ensemble means. Given inconsistency in shortwave timing the past several days, preferred to keep the system outside the 40/70 benchmark next Wed. In the West, the leading front into Washington on Sunday will weaken in favor of a stronger shortwave on its heels. The ECMWF continued to be more aggressive than the GFS and has wobbled farther south or north with each run. Trend does seem to give merit toward a stronger shortwave or possibly closed low. To the south, the closed low off Baja California may eventually get tugged back to the coast given enough digging of the incoming trough Tue/Wed through the West. This would act to lower heights over the Southwest via interaction/merging of the two features. Confidence is low in details due to timing uncertainties. Overall, a GFS/ECMWF/GEFS/ECMWF ensemble mean blend sufficed through much of the period. Trended increasingly toward the ensemble means due to their more modest depictions of the western troughing and exiting eastern system next week. ...Weather Highlights/Threats... Below average temperatures in the East on Sunday will slowly moderate back toward more typical mid-November values by Tuesday. Much of the West will have temperatures above normal by 5-15 degrees Sun-Tue before troughing brings in cooler temperatures within about 5 degrees of average. The lead system off the Mid-Atlantic coast should keep the heaviest rains offshore but could be close enough to produce some showers right along the coast. The strong pressure gradient between the low and the sfc high exiting New England will lead to windy conditions along the coast and especially over the nearshore waters. Please see the Ocean Prediction Center's products for more information. Second area of low pressure may bring rainfall farther west, depending on the track. Per the forecast, the precipitation shield will move northward into New England late Tue into Wed where temperatures may be cold enough for some snow in higher elevations Wed-Thu. Several systems out of the Pacific will maintain a rather wet period for at least coastal Washington/Oregon and the Cascades Sun-Wed. Lighter rain/snow along is forecast for areas along the Continental Divide and even lighter amounts into the High Plains. With increased troughing toward the Southwest next week, precipitation chances will increase Wed into Thu. Some rain is possible for the lower/coastal elevations of southern California into some of the deserts with higher amounts in the terrain. Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml